1. Field of the Invention
This invention relates to the process of recovering titanium values from waste generated in the process of machining titanium metal. In particular this invention relates to a process for recycling titanium grinding waste into an environmentally safe form for subsequent use in industrial processes requiring high titanium feed stock.
2. Description of the Related Art
The process of grinding titanium metal creates a residue of partially oxidized titanium metal fibers or slivers, commonly known in the industry as "swarf". In addition to swarf, the residue of the titanium grinding process contains, coarse trash, and grinding wheel fragments. As a waste by-product, grinding swarf is stockpiled for later disposal. Because titanium is a highly reactive material, it has been known for these swarf piles to spontaneously ignite. The resultant titanium oxide is extremely brittle and of little titanium value. Currently, there is no processing method to render the grinding swarf chemically stable to the environment. Accumulation of titanium grinding swarf is estimated to reach one million pounds per year. Recovery of titanium values from accumulating titanium grinding swarf would conserve a valuable resource and reduce problems associated with the accumulation of hazardous process waste material.
The titanium value may be recovered from grinding swarf by rechlorinating it, introducing it with titanium tetrachloride and reducing the mixture to titanium chloride. However, titanium chloride, has a lower market value compared to scraps of titanium metal mixed with the grinding swarf.
Processes and methods for recovery of iron units from flue dust are similar to the method described herein and are generally well known in the art. One such method is described in U.S. Pat. No. 4,407,672, issued Oct. 4, 1983, to Ruger A. Deuschle and Charles P. Mueller, entitled "Method for the Recovery of Iron Units from Flue Dust Generated in a Steel Making Process." Recovery of iron units from flue dust does relate to the problems of handling fine particle material but does not address the problems associated with highly reactive titanium and the need to keep materials out of the recovery process which could contaminate the final ferrotitanium and/or titanium slag produced. Also, Megy, U.S. Pat. No. 5,171,359 discloses a composition that reuses high purity titanium slivers, commonly known as swarf, produced by a wet grinding process. The titanium swarf, for use with the invention of Megy, is low in impurities such as oxides and nitrides. Megy does not disclose a process for treating a low grade milling waste that may contain grinding residue, titanium oxide, or coarse impurities.
The present invention overcomes the deficiencies in the prior art methods for recovering titanium values from what would otherwise be considered a waste by-product of the titanium and steel industries. It provides a method of handling and smelting titanium grinding swarf without contaminating on going ferrotitanium and titanium slag production processes. In addition to recovering titanium values from the grinding swarf, the problem of disposing the metallic waste is solved and the recovered titanium will increase concentrations of titanium in high titanium slag and ferrotitanium for the steel industry.